Mechanism of Cyanide

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The lethal poison cyanide causes death by interfering with cellular respiration. What is cyanide’s mechanism of toxicity?

A. Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen

B. Cyanide inhibits the binding of ATP to ATP synthase

C. Cyanide covalently binds to coenzyme Q (ubiquinone)

D. Cyanide breaks down the proton gradient across the inner mitochondrial membrane

Cyanide blocks the passage of electrons from cytochrome oxidase a3 to oxygen since it has a very high binding affinity for the enzyme. The cell cannot use oxygen so even if the person can breathe, the cells cannot use the oxygen that is delivered to tissues. Oligomycin inhibits the electron transport chain by directly affecting ATP synthase. A class of poisons called uncouplers makes the lipid bilayer permeable to hydrogen ions, which eliminates the electrochemical gradient.

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